1. Field of the Invention
The present invention relates to a dynamic pressure bearing device used in information equipment, acoustic equipment, video equipment, and the like.
2. Description of the Prior Art
As a prior art dynamic pressure bearing device, a structure disclosed, for example, in Japanese Patent Laid-Open Application No. 53-110746 has been known. This dynamic pressure bearing device is comprised of first and second members respectively having planes opposing each other. By forming a groove in the plane of the first member having a spiral shape for generating a dynamic pressure, air flows into the groove when the second member is rotated and a high pressure is generated so that the second member is rotated and a high pressure is generated so that the second member is rotated without contacting the first member. Furthermore, by forming a protruding portion in the form of a step of a minute size on the plane of the first member, the whole of both of the planes are prevented from directly contacting each other at the time of starting and stopping rotation.
However, the prior art dynamic pressure bearing device involves various problems as described below.
1) Although it is a dynamic pressure bearing device having a thrust bearing, a radial bearing is not included.
2) The protruding portion is in surface-contact with the plane of the second member, and thus, a large starting torque is required due to static friction existing therebetween. It also takes a long time to rise to a desired rotational speed.
3) On the other hand, sometimes, the second member is inclined with respect to the first member at the time of starting and stopping. As a result, a peripheral edge portion of the protruding portion is brought into contact with the plane of the second member and non-uniform contact tends to be caused resulting in large friction forces.